1. Field of the Invention
This invention relates to new and useful acid-curing binder compositions comprising furfuryl alcohol prepolymers and/or furfuryl dibasic acid diester compositions for use in the formation of sand cores and molds for foundry operations.
2. Description of the Prior Art
In the foundry industry, sand is coated with resin binders and formed into molds and cores for the production of precision castings. A wide variety of techniques has been developed for the manufacture of sand cores and molds. These involve the hot box technique for mold and core formation; the shell method; the "No-Bake", and the cold-box technique.
In the hot box and shell methods, sand molds and cores are formed by heating a mixture of sand with a thermosetting resin at a temperature of about 150.degree.-320.degree. C. in contact with patterns which produce the desired shape for the mold or core. The resin is polymerized and a core or mold is formed. Procedures of this type are described in Dunn et al U.S. Pat. No. 3,059,297 and Brown et at U.S. Pat. No. 3,020,609.
A particular disadvantage of the hot box and shell methods is the necessity for heating the pattern boxes to 150.degree.-320.degree. C. to polymerize and cure the resin binder. This involves considerable expense and is generally a high cost technique.
The cold box techniques for core and mold formation involve the use of sand mixed or coated with resins which may be cured at room temperature by acid or base catalysis. Acid or base catalysts have been used in liquid, solid or gaseous form. Typical cold box processes are shown in Blaies U.S. Pat. No. 3,008,205; Dunn et al U.S. Pat. No. 3,059,297; Peters et al U.S. Pat. No. 3,108,340; Brown et al U.S. Pat. No. 3,184,814; Robins U.S. Pat. No. 3,639,654; Australian Pat. No. 453,160 and British Pat. No. 1,225,984. Many of these processes involve the use of sulfur-containing acid catalyst such as benzene sulfonic acid, toluene sulfonic acid and the like.
Richard U.S. Pat. No. 3,879,339 discloses coating sand with an organic peroxide and resin, forming into a mold or core and gassing with sulfur dioxide.
A number of U.S. and foreign patents disclose the use of furfuryl alcohol and other furfuryl-substituted compounds in resin polymerization and also the use of dibasic acids and some esters in resin compositions.
Bradley U.S. Pat. No. 2,238,030 discloses the use of dialkenyl esters of dibasic acids in the copolymerization of addition polymers.
Dannenberg U.S. Pat. No. 2,650,211 discloses polymers including dibasic acids as precursors.
Treat U.S. Pat. No. 2,999,829 discloses the copolymerization of furfuryl alcohol and maleic anhydride in the preparation of foundry cores.
Case U.S. Pat. No. 3,312,650 describes resins based on phenol and furfuryl alcohol modified with formaldehyde and treated with an acid catalyst.
Kirkpatrick U.S. Pat. No. 3,244,770 discloses the use of diesters of dibasic acids in phenolic resin compositions.
Bean U.S. Pat. No. 3,248,276 discloses the use of dibasic acids in resin compositions containing condensation-type resins.
Guyer U.S. Pat. No. 3,404,118 discloses the use of furfuryl glycidyl ether in molding resins.
Fitko U.S. Pat. No. 3,600,290 discloses the use of unsaturated esters in resin compositions.
Adkins U.S. Pat. No. 3,725,333 discloses the preparation of foundry molds, etc. using phenolic resins modified with furfuryl alcohol.
Laitar U.S. Pat. No. 4,052,301 discloses resins for sand cores or molds by incorporating furan into a furfuryl alcohol-modified phenolic resin prepolymer.
Anderson U.S. Pat. No. 4,083,817 discloses the acid curing of mixtures of furan-formaldehyde resins with phenolic resins for production of foundry cores and molds.
Stewart et al U.S. Pat. No. 4,176,114 discloses acid curing condensation-type resins comprising a high viscosity polyfurfuryl alcohol alone or in admixture with phenol-formaldehyde or urea-formaldehyde or phenol-urea-formaldehyde precondensate resins, or cocondensates of polyfurfuryl alcohol with said precondensate resins. Such binders are useful for manufacturing sand cores and molds.
Gardikes et al U.S. Pat. No. 4,371,648 discloses binder compositions comprising furfuryl alcohol and a ester of a polyol and resin acid. The binders may also contain modifying agents such as furan polymers, urea-formaldehyde polymers and mixtures thereof.
British Pat. Nos. 626,763 and 922,345 disclose the use of glyceryl esters and other esters of aliphatic dibasic acids in condensation polymers.
The bis(tetrahydrofurfuryl) ester of adipic acid is known but does not undergo condensation type polymerization.
The above noted patents, however, do not consider the problem of the preferential polymerization of furfuryl alcohol when admixed with phenolic and other condensation-type resins and the problem of short bench life, or any way to overcome these problems.
In my copending patent application, Ser. No. 306,965, filed Sept. 30, 1981, dibasic acid diesters of the composition EQU R.sup.1 O.sub.2 C(CH.sub.2).sub.n CO.sub.2 R.sup.2
where n is from 1 to 8, R.sup.1 is furfuryl, and R.sup.2 is furfuryl or methyl, are disclosed as novel compounds and are also shown to be useful modifiers for various condensation-type and acid curable foundry resins. The Diesters are preferably added in the amount of 5-35 percent by weight of total composition. These compositions are particularly useful in the preparation of sand cores and molds for foundry use which have improved strength and hardnss. These furfuryl esters are also acid-curable and can be used alone as resin binders.